An agricultural harvester typically includes a self-propelled vehicle on which an engine and various pieces of auxiliary equipment are mounted. The engine, through several drive trains, drives the auxiliary equipment on the agricultural harvester which typically includes a large threshing rotor, cleaning fans, drive wheels, straw choppers, straw walkers, sieves, chaffers, and headers, among other devices.
Many of these devices are driven by mechanical devices such as gear boxes, rotating shafts, belts, pulleys, and hydraulic pumps connected to the engine. In one common arrangement, the engine is coupled to the large threshing rotor and to the cleaning fan by a drive train which includes a series of mechanical drive elements such as gear boxes driven by rotating shafts, belts and pulleys. In a common arrangement, one or more pulleys, having a variable pulley diameter, is disposed in the drive train between the engine and the threshing rotor or the cleaning fan, to control the speed of the rotor or the cleaning fan with respect to the engine.
One drawback of these variable pulleys is their slow response time. When a signal is sent to the variable pulley to command a change in its diameter, and thus a change in its speed relative to the engine speed, it takes a relatively long amount of time to affect this change. Variable pulleys cannot tolerate rapid changes in pulley diameter under load without suffering undue wear to the belt and pulley.
For this reason, adjustments are seldom made to the variable pulley diameter. Changes in the diameter of the variable pulley function to change the speed of the rotor or the cleaning fan with respect to the engine. As a general matter, the operator typically selects a new desired speed of the rotor or the cleaning fan, and the control system that controls the diameter of the pulley then establishes a new pulley diameter that will provide that new desired speed (assuming the engine keeps running at the same speed). The control system then stops adjusting the diameter of the pulley, at least until the operator requests a new desired speed.
If the load on the agricultural harvester increases, such as by running into a heavy crop or starting to climb a hill, then the engine speed will drop. When the engine speed drops, the rotor speed and the cleaning fan speed drop proportionally.
Similarly, if the load on the agricultural harvester is reduced, for example, by the crop thinning or the harvester starting to go downhill, the engine speed will increase. When the engine speed increases, the rotor and the cleaning fan speed increase proportionately.
In one prior art arrangement, the operator is able to select a desired new speed of the rotor or the fan using an operator input device such as a button, a knob, or a lever to select a desired new rotor or fan speed. In response to this, a control system increases or decreases the diameter of the variable pulley over a period of several seconds, until the speed of the rotor or fan reaches the desired new speed. Once the control system determines that the rotor or fan speed is at the desired new speed, it stops adjusting the diameter of the variable pulley. From that time on, as the engine speed changes, the rotor or fan speed changes proportionately, and the control system makes no further adjustment to the diameter of the variable pulley.
Unfortunately, this algorithm, while relatively simple, will not always give the results the operator anticipates. For example, since it takes a finite but nontrivial period of time for the control system to change the diameter of the pulley, occasionally the engine speed changes at the same time.
To illustrate the problem from the operator's perspective, imagine the following situation. The cleaning fan is operating at 1150 rpm and the engine is operating at 2300 rpm. The operator desires to reduce the fan speed to 1050 rpm, and operates the operator input device to select this speed. The control system, responding to the operator input device, begins the process of changing the diameter of the pulley to reduce the speed of the fan.
Shortly after the operator selects a desired new speed of 1050 rpm, the engine experiences a heavy load and the engine speed drops to 2100 rpm. When the engine speed drops to 2100 rpm, the cleaning fan speed drops automatically and coincidentally to the new target speed of 1050 rpm since the engine and the cleaning fan operate at speeds that are strictly proportional due to the fixed ratio gear train that couples them together.
The control system, even if it has made no change in the diameter of the pulley, senses that the fan is now running at the desired new speed of 1050 rpm. At this point, the control system ceases to adjust the diameter of the variable pulley, assuming that the control system adjustments are complete, based on the cleaning fan operating at the desired new speed. The control system stops adjusting the diameter of the pulley, even though it has made no adjustment to the diameter of the variable pulley.
The operator will immediately notice this failure to go to the desired new speed when the engine shortly recovers from its increased load and speeds back up to its normal operating speed of 2300 rpm. When this happens, the cleaning fan will again return to its original operating speed of 1150 rpm. The control system in effect mistakes the change in the cleaning fan speed caused by a temporary drop in the engine speed as actually setting a desired new cleaning fan speed.
What is needed in the art is a system for accommodating changes in engine speed while an adjustment is made to the cleaning fan (or threshing rotor) speed so that the operator's natural expectations are preserved.